Vehicle bodies are generally comprised of stamped or molded body members. These body members most often are made of steel, however, other materials such as aluminum or plastic may also be used.
Methods for joining the body members may include welding, riveting, using mechanical fasteners, and crimping or clinching parts together. Riveting and using mechanical fasteners join discrete portions of the body members together. Similarly, weld joints are often made at spaced intervals, rather than continuously, to reduce the cost of assembling the vehicle body.
One disadvantage to joining body members together only at discrete locations, as compared to using continuous joints, is that the vehicle body then has a reduced rigidity or stiffness. Ideally, the vehicle body would be as rigid as possible to limit deflections of the vehicle body. Further, increasing the vehicle body stiffness raises the natural frequencies and changes the modes of vibration of the vehicle body.
The largest forces input to the vehicle body during normal vehicle operation are ground forces, such as those caused by hitting a pothole or running over rough terrain. These forces are transferred through the vehicle suspension system to the vehicle body. While relatively large in magnitude, these forces are usually associated with low frequencies.
Accordingly, by making the vehicle body very stiff and raising the natural frequencies of the body components and vehicle body, the ground forces are less likely to cause a resonant condition to occur in the vehicle body.
Another source of forces input to the vehicle body is the vehicle drivetrain. These forces are generally smaller in magnitude than the ground forces but higher in frequency.. Again, it is advantageous to increase vehicle body stiffness to reduce the effects these forces have on the vehicle body.
The above-described methods of joining body members together to construct and stiffen a vehicle body have numerous shortcomings. First, stiffening a vehicle body by adding large, continuous welds between body members introduces significant additional weight to the vehicle body which is undesirable. A further disadvantage to using welding is that not all materials are readily weldable together to form strong joints. Aluminum and plastics are good examples. Adding stiffness by increasing the number of mechanical fasteners, such as bolts, rivets, or clips, also adds significant weight while increasing the complexity and cost of construction.
One method of increasing stiffness while adding little overall weight to a vehicle body is by using adhesive joints. Adhesive joints can provide a virtually continuous connection between body members, thereby increasing stiffness, while doing so with only thin layers of adhesives forming bonds between the body members. Consequently, very little weight is added to the overall vehicle body. In the event some of the welds or mechanical fasteners are replaced with adhesive joints, the overall weight of the vehicle body may actually decrease.
However, using adhesive joints also has its drawbacks. First, the adhesive joints are often located in regions where the joints are not visible after vehicle body assembly. Accordingly, checking on the quality or integrity of the joint is difficult. These hidden joints may be inspected for the presence of adhesive using ultrasonic equipment. However, such evaluation is time consuming and expensive.
To quickly cure these adhesive joints, the vehicle bodies are placed in curing furnaces. After removal from the curing furnace, as the adhesive joints are hidden, they are difficult to inspect to insure that proper curing has indeed occurred.
Another method of ensuring that an adhesive bond joint is present is by providing excessive adhesive and checking to see that adhesive is squeezed from between free edges of the body members. This method is messy and wastes adhesive. Excessive adhesive located on exposed surfaces can cause gumming and may adversely affect welding apparatus or other fastening equipment. Accordingly, this method is also undesirable.
For the foregoing reasons, there is a need for a vehicle body construction which utilizes a low cost reliable method for inspecting adhesive bonds or joints between body members. The present invention is intended to minimize the above-described shortcomings of previous vehicle body constructions and their methods of manufacture.